This invention relates generally to lasers, and, more particularly, to an annular optically pumped laser which incorporates therein adjustable as well as interchangeable windows.
Lasers are now well established in the art for generating coherent electromagnetic radiation in the optical frequency range. The operation of a laser is based upon the fact that the atomic systems represented by the atoms of the laser material can exist in any of a series of discrete energy level or states, the systems absorbing energy in the optical frequency range in going to a higher state and emitting it when going to a lower state. In the case of ruby as a laser material, three energy levels are utilized. The atomic systems are raised from the lower or ground level to the higher of the three levels by irradiation from a strong light source which need not be coherent but should preferably have a high concentration of energy in the absorbing wavelengths. A radiationless transition then occurs from the highest state to an intermediate or metastable state. This is followed by a transition with photon emission from the intermediate state back to the ground state. It is the last transition that is of interest since this transition is the source of the coherent light or electromagnetic energy produced by the laser.
The operation of raising the energy level of the laser material to produce the desired photon emission is referred to in the art as "pumping" and when more atoms reach an excited metastable state than remain in a lower energy level, a "population inversion" is said exist.
The active material in the laser is made optically resonant by placing reflectors at either end thereof to form a resonant cavity. The reflector on at least one end is made partially transmissive so that there will be an escape from the resonant cavity of a laser beam.
Gas lasers are generally made up of an elongated hollow tube sealed at both ends thereof by a pair of laser windows and filled with any suitable laser reactant mixture. Adjacent the sealing windows are situated the reflective surfaces, forming therebetween the resonant cavity. The lasing action takes place upon the application of a suitable pumping pulse to the laser reactants. The pumping pulse may be in the form of a flash of intense light. For proper operation of the laser, it is extremely important that the positions of the laser windows and the reflectors which form the resonant cavity be precisely aligned.
In the prior art many alignment devices have been used for laser mirrors, unfortunately these devices where unacceptable for the purpose of aligning the laser windows since the seal between the laser windows and the end of the laser tube must hermetically seal the interior of the tube, and, must prevent the release of gaseous impurities into the tube.
In addition to the above criteria it would be extremely practical if the laser windows were not only adjustably mounted to the laser head, but also mounted in such a manner as to permit their rapid and easy removability for purposes of interchanging a plurality of laser windows. Such a design would allow the laser to be used as a basic tool in the study and/or evaluation of annular optics.
Heretofore, the effectiveness of adjustable laser windows left much to be desired. In addition to their cumbersome and complex construction many problems resulted in maintaining proper sealing of the windows once the window was adjusted or positioned on the laser head. It is therefore clearly evident that not only is there a need for a laser having easily adjustable windows, but there is also an added economic benefit which can be derived if the laser head is capable of reliably accepting a plurality of various laser windows.